Collective Code Ownership is an idea that everyone owns the code. It encourages that the whole team contributed with ideas and every developer can change, fix bugs, improve design and refactor.
There is no “chief architect” that you need to ask for answers or permission. Collective ownership when it works is much more powerful, engaging and empowering than putting one person in charge. And when you have one person in charge you take away the responsibility from the team.
With this you minimize key dependence from team members.
Start to talk about what this means for your team, and when you could adopt it. Then you induce them to share and engage in each others code.
Read more at Extremeprogramming
Thanks to Jimmy Janlén for letting me use his pictures from Agile Topics Cards.
Agile Cook Book 